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COMPARISONS OF THE RESULTS FROM STATIC PENETRATION TESTS AND LARGE IN-SITU PLATE TESTS IN LONDON CLAY

The paper describes investigations in which the results of static cone penetration tests in fissured London Clay are compared with large in-situ plate tests and laboratory tests on samples removed with a minimum of disturbance. The end bearing pressures measured on 35.6 mm diameter cones in London Clay are dependent on the rate of penetration, particularly over the range of rates in common use. Bearing pressures measured on cones penetrating at a rage of 1200 mm/min were approximately 2.5 times those measured on 865 mm diameter plates for which the rate of penetration was 2.5 mm/min. Even after allowance was made for the different rates of penetraion the cones gave bearing pressures approximately twice those measured on large diameter plates. The author considers that these large differences were mainly due to the scale effects arising from the macro- structure of the clay. Differences also arise from the different stress levels acting around a 'driven' probe and a loaded plate installed in a borehole. It is shown that correlations between cone penetration tests and laboratory tests are unreliable since both are affected by the size of the macrostructure of the clay.

Supplemental Notes:

This paper was submitted to the European Symposium on Penetration Testing, Stockholm, June 1974, and will subsequently appear in the Proceedings.